In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
Future generations cellular communications networks are expected to provide high data rates, up to several Gbps while at the same time be energy efficient. One way to achieve such high data rates and/or to lower the energy consumption in cellular communications networks is to deploy reconfigurable antennas systems (RAS). In general terms, a RAS may be defined as an antenna system whose radiation characteristics can be changed by nodes in the network after deployment, inter alia to be adapted to current traffic needs in the communications network. One common antenna parameter that can be remotely controlled is the antenna tilt. It is foreseen that technology advances may introduce possibilities to modify the antenna lobe shapes, beyond the (one-dimensional) antenna tilt. For example, the antenna system may then be reconfigurable to better serve a traffic hotspot by, inter alia, increasing the antenna gain toward the hotspot location. RAS may be automatically controlled, for example by the use of a sell-organizing network (SON) algorithm. RAS controlled by SON algorithms are hereinafter called RAS-SON.
In general terms, RAS is to be distinguished from beamforming specific for a wireless device (so-called device-specific beamforming). In this respect, RAS is used to shape the cell-specific beam patterns for cell-specific reference signals (CRSs) and control signals, and is typically changed quite slowly, accommodating for changes in the infrastructure or user behaviors, for example on an weekly basis. In contrast, device-specific beamforming is used to shape the beams for device-specific signals and is typically changed very quickly, for example on a millisecond basis.
In order to enable efficient coordinated multi-point (CoMP) schemes future releases of the long-term evolution (LTE) telecommunications standard may enable the possibility to configure wireless devices to report received signal powers based on measurements on a configured set of channel state information-reference signals (CSI-RS) and channel state information-interference measurement (CSI-IM) resources (where the CSI-IM resources corresponds to CSI-RS resources in neighboring cells), see A3GPP TS36.213 V10.4.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”. Hereinafter the received signal power measurements based on either CSI-RS or CSI-IM resources are denoted as CSI-RS received power (CSI-RSRP).
It is possible in LTE to obtain path gain measurements between network nodes and wireless devices by using reference signal received power (RSRP) measurements that are based on the CRS signals. The network node can then test different antenna settings, e.g. the tilt, of the CRS signals and request the wireless devices perform RSRP measurements on each of the tilt settings. However, by changing the tilt of the CRS signals, the network node will change the coverage of its cells (i.e., the regions in which the network node provides network coverage) which might lead to dropped users and deteriorated user experience.
Another way to measure path gains for different antenna patterns is to use uplink sounding reference signals (SRS). One issue with this approach is that the network nodes do not know which output power the wireless devices use; hence it is not possible to calculate the path gains. Another issue is that due to the output power control algorithm used by the wireless devices, some of the wireless devices might have very low output power (typically wireless devices close to a serving network node) which will make it difficult for network nodes located far away from the wireless device to perform reliable path gain measurements.
In conclusion, tuning RAS settings for network nodes in a communications network by using SON-algorithms may be very time consuming and can take several weeks for a large area. One reason why it could take so long time is that there exist many different combinations of possible RAS settings in a network and each RAS setting typically needs to be evaluated during quite long time (such as hours or days) in order to gather enough statistics. Moreover, network performance degradations (also called icicles) may occur when evaluating many different combinations of candidate antenna settings.
Hence, there is still a need for an improved determination of antenna settings, such as radiation beam patterns.